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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Dates equality check fails when a date is folded and the other is not","articleBody":"# Bug report\r\n\r\n### Bug description:\r\n\r\nIn the example I have two dates in the Europe/Rome format, representing 2:00 AM on a day with DST change. One of the dates is folded, the other is not.\r\n\r\n```python\r\nfrom datetime import datetime\r\nfrom zoneinfo import ZoneInfo\r\n\r\nnot_folded = datetime(2023, 10, 29, 2, 0, tzinfo=ZoneInfo(\"Europe/Rome\"))\r\nfolded = datetime(2023, 10, 29, 2, 0, tzinfo=ZoneInfo(\"Europe/Rome\"), fold=1)\r\n\r\nprint(\"Not folded date: \", not_folded.isoformat())\r\nprint(\"The folded date: \", folded.isoformat())\r\n\r\nassert folded != not_folded\r\n```\r\n\r\nThe two dates are different, as the isoformat() print shows, and they represent a different moment in time (one is 00:00 UTC, the other one is 01:00 UTC). However, the assert fails:\r\n```\r\nNot folded date:  2023-10-29T02:00:00+02:00\r\nThe folded date:  2023-10-29T02:00:00+01:00\r\nTraceback (most recent call last):\r\n  File \"/Users/alerinaldi/prova.py\", line 10, in \u003cmodule\u003e\r\n    assert folded != not_folded\r\n           ^^^^^^^^^^^^^^^^^^^^\r\nAssertionError\r\n```\r\n\r\nOf course, this also applies to other situations where dates are compared: I discovered the issue while memoizing the result of a function based on dates using a dict.\r\n```python\r\nfrom datetime import datetime\r\nfrom zoneinfo import ZoneInfo\r\n\r\n__memoized_dict = {}\r\n\r\n\r\ndef process_date(dt: datetime) -\u003e int:\r\n    return int(dt.timestamp())\r\n\r\n\r\ndef memoized_result(dt: datetime) -\u003e int:\r\n    if dt in __memoized_dict:\r\n        return __memoized_dict[dt]\r\n    res = process_date(dt)\r\n    __memoized_dict[dt] = res\r\n    return res\r\n\r\n\r\nprint(memoized_result(datetime(2023, 10, 29, 2, 0, tzinfo=ZoneInfo(\"Europe/Rome\"))))\r\nprint(memoized_result(datetime(2023, 10, 29, 2, 0, tzinfo=ZoneInfo(\"Europe/Rome\"), fold=1)))\r\n```\r\n\r\nThe second call returns a wrong result.\r\n\r\n### CPython versions tested on:\r\n\r\n3.12\r\n\r\n### Operating systems tested on:\r\n\r\nmacOS","author":{"url":"https://github.com/ale-rinaldi","@type":"Person","name":"ale-rinaldi"},"datePublished":"2024-02-23T09:23:44.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":3},"url":"https://github.com/115845/cpython/issues/115845"}